The present invention relates to the field of quality-of-service (QoS) support for applications such as adaptive real-time services running on mobile devices, which are used to support different access technologies in dynamic, mobile, wireless IP networks where the quality of the node connectivity can be unpredictably time-varying.
A source of temporary network resource degradation is the bandwidth-constrained wireless link level performance. Due to radio link characteristics and impairments, connections between mobile nodes can be time-varying. Unpredictable time-varying link quality has negative effects on the connectivity between adjacent nodes and terminal access to the network as well.
A further source of unreliability lies in a potentially unpredictable availability or movement behavior of wireless nodes, which belong to an intermediary transport network, e.g. a third-party network. Mobile networks beyond 3G may extend fixed wireless network access infrastructure with wireless ad-hoc networks to extend radio coverage and network capacity for mobile users. An architecture comprising wireless access routers or even mobile terminals has been investigated by the European project MIND (see IST-2000-28584 MIND, Mobile IP-based Network Developments, http://www.ist-mind.org/). The removal or switch off of wireless network nodes such as wireless routers or mobile terminals could leave behind a separated network branch that has been cut off from public access. As a consequence, transport quality along a dedicated path through a network might change over time quite frequently and significantly.
Hence, existing QoS-sensitive flows have to be rapidly established, restored, adapted and released in response to wireless impairments as well as topology changes. As described in the article “A Framework for Bidirectional QoS Signaling” (Internet Draft, 2002) by S. M. Shahrier and K. M. Shaheen, this problem counteracts the principle to support real-time conversational applications, e.g. voice-over-IP (VoIP) or videoconferencing, with performance requirements similar to those of existing circuit-switched or voice-based wired and wireless systems because all these symmetric streaming services impose stable symmetric bidirectional resource requirements, e.g. bandwidth and latency characteristics.
The complexities of existing protocols often do not meet these requirements. Service architectures have been proposed to enable resource reservation for an individual data flow (e.g. file exchange with an ftp server), namely the Integrated Services (IntServ) model. Alternatively, the Differentiated Service (DiffServ) model has been proposed to improve scalability by determining packet forwarding behavior on aggregates of flows with less state information required in network nodes along the routing path. The resource reservation protocol (RSVP) as one candidate of the IntServ model has been proposed to enable an application to spontaneously signal resource demands to a peer host. The protocol may be interpreted hop-by-hop along the routing path or tunneled transparently to a non-RSVP network region with appropriate mapping mechanisms in place at the network boundaries of the non-compliant region. Though the RSVP protocol has gained some acceptance in IP-related research and standardization communities, deficiencies of the protocol become obvious when it has to interoperate with adaptive real-time applications in mobile environments. Even ongoing standardization to extend RSVP (as investigated in IETF WG NSIS) can not sufficiently compensate the described networking problems since a clear separation between control and user data does not allow fast adaptation to changed networking conditions.
At the local level, ad-hoc networks that link notebook or palmtop computers could be used to spread and share information among participants of a conference. They might also be appropriate for applications in home networks where devices can communicate directly to exchange information, such as audio and/or video signals, alarms, and configuration updates. Perhaps the most far-reaching applications in this context are more or less autonomous networks of inter-connected home robots that clean, do dishes, mow the lawn, perform security surveillance, and so on. Recently, ad-hoc multi-hop networks were proposed for environmental monitoring, in which said networks could be used to forecast water pollution or provide early warnings of an approaching tsunami. Short-range ad-hoc networks can simplify intercommunication between various mobile devices (e.g. cellular phones and PDAs) by forming a so-called “Personal Area Network” (PAN), thereby eliminating the need for cables. This could also extend the mobility provided by fixed networks to nodes of an ad-hoc network domain.
Typically, mobile ad-hoc networks (MANETs) operate with distributed functions and allow traffic to pass over multiple radio hops between a source and a destination. Routing algorithms and the implications of radio layers are challenging research areas for these networks. The inherent unpredictability in a network whose nodes move poses a challenge to routing and mobility functions if data is consistently transferred between the nodes of the underlying network. Nonetheless, multi-hop radio systems also make it possible to save battery capacity while retaining performance. In any case, the most attractive property of an ad-hoc networking model is perhaps its independence from centralized control and, thus, the increased freedom and flexibility it gives the user.